1. Field of the Invention
The present invention relates to a valve operating system in an internal combustion engine comprising a swinging support section provided at a base end of a rocker arm and swingably carried on an arm support portion provided in a cylinder head, a plurality of valve abutments provided at a tip end of the rocker arm and capable of being individually put into abutment against upper ends of a plurality of engine valves, and cam abutments provided on the rocker arm in an intermediate portion thereof between the swinging support section and the valve abutments to come into contact with a valve operating cam.
2. Description of the Related Art
Such a valve operating system is conventionally known, for example, from Japanese Patent Application Laid-open No.6-185322.
In a valve operating system which is designed such that a plurality of engine valves are driven by a single rocker arm, the width of the rocker arm cannot help increasing, thereby bringing about increases in size and weight of the rocker arm. In the mentioned known system, however, a structure for reducing the weight of the rocker arm is not disclosed.
Accordingly, it is an object of the present invention to reduce the weight of the rocker arm for driving the plurality of engine valves.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a valve operating system in an internal combustion engine comprising a swinging support section provided at a base end of a rocker arm and swingably carried on an arm support portion provided in a cylinder head, a plurality of valve abutments provided at a tip end of the rocker arm and capable of being individually put into abutment against respective upper ends of a plurality of engine valves, and cam abutments provided on the rocker arm in an intermediate portion between the swinging support section and the respective valve abutments to come into contact with a valve operating cam, wherein the rocker arm has wall-removed portions formed therein at locations corresponding to the cam abutments, the wall-removed portions opening at opposite sides of the rocker arm.
With such arrangement of the first feature, the weight of the entire rocker arm can be reduced by the wall-reduced portions provided at the locations corresponding to the cam abutments.
According to a second aspect and feature of the present invention, in addition to the first feature, the rocker arm includes an opening in which a roller which is the cam abutment is accommodated, and a pair of coaxially disposed shaft insertion bores with its inner ends thereof opening into the opening and with its outer ends opening outwards and sideways of the rocker arm for fitting and fixing of opposite ends of a roller shaft for rotatably supporting the roller, the roller shaft being fitted and fixed in inner ends of the shaft insertion bores, with portions of the shaft insertion bores axially outer than the opposite ends of the roller shaft being left as the hollow wall-removed portions.
With the arrangement of the second feature, the portions of the shaft insertion bores axially outer than the opposite ends of the roller shaft are left as the hollow wall-removed portions, whereby the weight of the entire rocker arm can be reduced and moreover, the length of the roller shaft can be reduced. Thus, it is possible to facilitate the assembling of the roller shaft to the rocker arm and to make the roller shaft difficult to deform, thereby ensuring the proper swinging operation of the rocker arm.
According to a third aspect and feature of the present invention, in addition to the second feature, each of the shaft insertion bores comprises a first insertion bore portion adjacent to the opening, a second insertion bore portion connected at an inner end thereof to an outer end of the first insertion bore portion, and a step formed between the outer end of the first insertion bore portion and the inner end of the second insertion bore portion and facing on a side opposite to the opening, and the opposite ends of the roller shaft fitted respectively in the first insertion bore portions of the shaft insertion bores are disposed in caulked engagement with the step.
With such arrangement of the third feature, the size of each of the wall-removed portions of the shaft insertion bores left as the hollow form can be increased, thereby further reducing the weight of the entire rocker arm. Moreover, the roller shaft can be fixed to the rocker arm by caulking and hence, it is possible to further facilitate the assembling of the roller shaft to the rocker arm.
According to a fourth aspect and feature of the present invention, in addition to the second feature, the rocker arm has a pair of support walls provided thereon to extend from the swinging support section in such a manner that the valve abutments individually corresponding to the pair of engine valves are provided at tip ends of the support walls, and the opposite ends of the roller shaft formed at a length shorter than a distance between both of the support walls are fitted and fixed in the shaft insertion bores such that the wall-removed portions can be formed in the rocker arm at locations axially outer than the opposite ends of the roller shaft.
With the fourth feature, loads from the engine valves are applied to the support walls, but the roller can be supported by the roller shaft disposed at a location kept away from portions to which the loads are applied and hence, the rigidity of supporting of the roller can be enhanced.
According to a fifth aspect and feature of the present invention, in addition to the fourth feature, the rocker arm has a pair of cylindrical shaft support portions provided thereon over the first and second support walls and the opening to define the shaft insertion bores, respectively. With such arrangement of the fifth feature, the pair of the cylindrical shaft support portions interconnected through the roller shaft are connected to the support walls and hence, the rigidity of support walls and the rigidity of supporting of the roller can be enhanced.
According to the sixth aspect and feature of the present invention, in addition to any of the second to fourth features, each of portions of the shaft insertion bores left as the wall-removed portions is formed into such a shape that it is enlarged gradually as approaching the side of the rocker arm.
With such arrangement of the sixth feature, it is possible to facilitate an operation for fitting and fixing the roller shaft in the inner ends of the shaft insertion bores, leading to an enhanced assemblability.
According to the seventh aspect and feature of the present invention, in addition to the first feature, the rocker arm has a pair of support walls provided thereon to extend from the swinging support section in such a manner that the valve abutments are provided at tip ends of the support walls; a cam slipper which is the cam abutment is provided on the rocker arm between both of the support walls; and the wall-removed portions are formed within a pair of connecting tubes which interconnect the support walls and the cam slipper.
With the arrangement of the seventh feature, the cam slipper is continuously formed with the pair of support walls through the pair of the connecting tubes. Therefore, it is possible to reduce the weight of the rocker arm, while avoiding reductions in rigidity of the support walls and the rigidity of supporting of the cam slipper.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.